In many electronic applications, it is necessary to connect two metal surfaces in order to properly ground two separate components. These components can be items like IC chips, packages, hybrid components, multichip modules, printed circuit boards, ceramic substrates, heat sinks, chassis and housings. It is often impractical or impossible to mechanically secure the two components with screws or clamps, in which case it is desirable to use an electrically conductive adhesive.
Commonly, polymeric conductive adhesives, such as epoxy resins loaded with conductive particles, such as carbon or silver or the like, are used. However, particles in a resin matrix frequently do not achieve good conductive efficiency because over time the particles tend to shift in the resin matrix and change the conductivity. Furthermore, in applications where high conductivity is needed, the amount of particles in the adhesive needs to be high, e.g., as high as 80% filler in some instances. The large amount of particles is needed to insure particle to particle contact through the resin matrix. This high amount of particles causes the resin/filler combination to be brittle or of weak bond strength.
Because of the high surface resistance of particle to particle contact, applications that require high conductivity must use silver particles because other metals form oxides too readily and produce higher resistance adhesives. Moreover, when it is necessary to bond aluminum parts and high conductivity is required, there is a problem with using silver particles because the silver reacts galvanically with aluminum and causes corrosion to occur.